BAGHDAD, Iraq, May 9 — It was almost 3 a.m. in Zubaida Square in central Baghdad last week when headlights signaled one flash, then two, then one again.

From the darkness, someone signaled back. The watchers were there.

As evidence mounts that Shiite police commandos are carrying out secret killings, Sunni Arab neighborhoods across Baghdad have begun forming citizen groups to keep the paramilitary forces out of their areas entirely. In large swaths of western Baghdad, and in at least six majority Sunni areas in its center, young men take turns standing in streets after the 11 p.m. curfew, to send out signals by flashlights and cellphones if strangers approach.

In some cases, the Sunnis have set up barricades and have taken up arms against Shiite-led commando raids into their neighborhoods. In other cases, residents have tipped off Sunni insurgents. Watch groups have been assembled in other mixed areas, including Baquba to the north and Mahmudiya to the south, residents and officials said.

Three years after the American invasion, the war has settled here, in the quiet of neighborhoods, streets and Iraqis' backyards. Dozens of bodies surface daily. People are taken from their homes and executed. Assassinations are routine. But instead of looking to the government for protection, ordinary Sunni Arabs are taking up arms against it, perhaps the most vivid illustration of the depth of Sunni mistrust of the American backed, Shiite-led security forces. "There is no bridge of confidence between the government and the Iraqi people," said Tarik al-Hashimy, a vice president of Iraq who is a Sunni Arab.

It's only a matter of time before the boys take over protection. If you're already standing guard against the PD, why aren't you going after the Americans who back them? The guerrillas will be in the middle of this, sooner rather than later.